How does an owner who gets no paycheck make a deferral

An LLC shareholder taxed as a sole prop wants to contribute a deferral but he gets no paycheck. How is that accomplished?

Check? Money Order? ACH Debit? Wire Transfer?

Take your pick.

Charles, the LLC member ( business owner) would complete a deferral election form authorizing the deferral to be made.

From the business checking account said deferral amount will be sent to the 401(k) plan as Lou S. indicates.

The bookkeeping for the deferral on the employer side will be taken care with the partnership return and the K1.

It couldn't hurt to complete some sort of "deferral election," but it's a complete fiction in this context and if it hadn't been done I would be prepared to make the case before an IRS auditor that a sole proprietor can still have a good deferral election simply by writing a personal check for deposit to the plan.  

While I agree with Jpod that it is a bit of an administrative fiction in such a situation, I'd put it a little more strongly than "it couldn't hurt." I would absolutely recommend that there is a deferral election in place before writing a check, etc.

 The requirements of 1.401(k)-1(a)(6), which also refer you back to 1.401(k)-1(a)(3), are such that you may have a difficult fight with an IRS auditor if there isn't an actual "election" in place. If there isn't, then of course as Jpod suggests, you would have to make your case, but it is so easy to avoid trouble by putting an election in place prior to any contribution that I can't see a valid reason for not doing so. 

The LLC shareholder must make an irrevocable written election by 12/31. See 1.401(k)-1(a)(6)(iii). Then the amount elected is taken later from the LLC owner's share of the LLC's earned income, assuming the plan document provides for participation by self-employed persons and that the individual has earned income from the LLC for the year.

This LLC is a disregarded entity; it does not exist for tax purposes and the owner is treated as an unincorporated sole proprietor.  So, please enlighten us:  to whom should he be conveying his election?  Don't get me wrong; he should probably write a letter addressed to the LLC expressing his "election," sign it and date it and stick it in a drawer, but let's be real here, this is a complete fiction.  This scenario was intentionally side-stepped in the regulation you cited.      

1 hour ago, jpod said:

This LLC is a disregarded entity; it does not exist for tax purposes and the owner is treated as an unincorporated sole proprietor.  So, please enlighten us:  to whom should he be conveying his election?  Don't get me wrong; he should probably write a letter addressed to the LLC expressing his "election," sign it and date it and stick it in a drawer, but let's be real here, this is a complete fiction.  This scenario was intentionally side-stepped in the regulation you cited.      

Because a copy of deferral elections is one of the first things requested in an audit, he should complete the same deferral election form or online election as any other employees. That will keep auditors happy.

I'm guessing there are no employees and this is a retail solo plan set-up with no on-line election capability.

As an additional comment, if the sole prop makes his "deferral" contribution before the end of the year, the act of making the contribution to the plan will meet the requirement of a positive election by the year end; no additional paperwork would be necessary.  If contribution is NOT made by year end, then absolutely a document should be used to reflect the deferral amount.  The election can be (and should be) subject to the actual income when determined is at least that amount elected.

Charlie's question implied that this was a single member LLC and therefore disregarded entity, because it said the shareholder was taxed as a sole proprietor, but did not explicitly say that and did not refer to the shareholder as "sole shareholder," so I did not want to assume disregarded, although I agree that is very likely the case. I agree that the election is very fictional, but from IRS's perspective if there is no written election that says it was made on 12/31, the individual could wait until deep into the next tax year to decide whether he/she wanted to defer, which would be even more problematic for them I think.

There cannot be another owner if he is "taxed as a sole proprietor."

Right. Disregarded entity was pretty clearly implied.